The present invention relates to a cylinder head of an internal-combustion engine with at least one inlet valve and a fuel injection in an air-intake channel and with an evaporation element intended for improving the fuel/air mixture formation and projecting into the air-intake channel.
A cylinder head with an evaporation in the air-intake channel is described in U.S. Pat. No. 3,760,780. A resistance heating device is arranged on the evaporation element to improve the mixture formation. This resistance heater is equipped with a control for keeping the temperature of the element constant. In the higher load and speed ranges, however, the mixture mass flow also increases, with the result being that the evaporation element kept at a constant temperature can no longer heat the mixture mass sufficiently.
An object of the present invention is, therefore, while doing away with the resistance heating, to provide an evaporation element which heats the mixture mass as a function of the mixture mass flow, with more or less heating power being supplied respectively with an increasing or decreasing mixture mass flow.
This object has been achieved in accordance with the present invention by configuring the evaporation element to adjoin one end of a main engine combustion space and be made of a high thermal conductivity material.
Thus, in multi-valve engines, a cylinder constituted of high thermal conductivity material is fitted as an evaporation element in a partition wall between the inlet channels. The cylinder projects with one end into the main combustion space and with the other end into the air-intake channel. The evaporation element conducts some of the heat occurring during combustion in the main combustion space directly into the air-intake channel, and this is utilized for heating the mixture mass.
With the use of the evaporation element according to the invention, a self-regulating effect on the surface temperature of the heating element and on the mixture mass temperature is achieved, since, for example when there is an increasing mass flow because of the greater combustion heat associated therewith, an increasing transmission of heat into the air-intake channel takes place. Furthermore, a resistance heating with temperature control of previous versions of an evaporation element is avoided and the power supply of the motor vehicle is relieved.
According to another feature of the present invention, the evaporation element additionally possesses, within the partition wall, an annular clearance which largely prevents direct contact of the element with the partition wall and which therefore reduces heat-transmission losses.
A surface enlargement via a ribbed configuration of the end projecting into the air-intake channel further improves the heat emission of the evaporation element.
In an especially streamlined embodiment of the present invention, the end of the evaporation element projecting into the air-intake channel is made oval in cross-section.
By the formation of an air-insulating gap between the ribbed end of the evaporation element terminating flush with the contour of the partition wall and the surrounding partition wall, the fraction of combustion heat transferred from the evaporation element to the surrounding partition wall is reduced and the heating power is consequently increased.